What is Plato's Analogy of the Cave?

The Analogy of the Cave is a model Plato used in Book VII of The Republic to explain his metaphysical Theory of the Forms  

It is composed of four key elements:-

The sun represents the Form of the Good. Just as the Form of the Good is the source and origin of all the other forms, the sun’s light and heat is the source and origin of all life.

The cave represents the ‘World of Appearances’ (physical world) which Plato insists we live in presently, vs the outside world which represents the ‘World of Forms’ where true knowledge presides, and which our soul has been to before our physical life.

The shadows on the wall of the cave represent the illusory nature of the physical world. Things in the physical world are only likenesses or ‘shadows’ of the Forms.

The prisoners represent people trapped in their false perception of reality, and those who are unable to see the World of Forms. 

There are many other elements to this rich and complex analogy, but these are the key features.